1. Field of the Invention
The present invention relates to an electromagnetically reciprocating apparatus which is used as, for example a fluid pump.
2. Description of the Related Art
Fundamental construction of one example of a conventional electromagnetically reciprocating apparatus, which is used as a fluid pump (compressor, vacuum pump), is shown in FIG. 1. The conventional apparatus comprises: electromagnet 100, which is consisted of iron core 100a and coil 100b and repeats magnetization and demagnetization for one cycle of AC current; piston assembly 102, which includes magnetic material member 102a to be drawn by magnetized electromagnet 100, and front and rear pistons 102b, 102c disposed before and behind magnetic material member 102; front and rear cylinders 104, 106 for supporting front and rear pistons 102b, 102c of piston assembly 102; and a compression elastic member, in the form of a compression coil spring 108, which is compressed by piston assembly 102 when the latter is moved in a forward direction (movement in a rightward direction in FIG. 1) by magnetic action of electromagnet 100, and which moves piston assembly 102 in a backward direction (movement in a leftward direction in FIG. 1) by elastic force when electromagnet 102 is demagnetized.
In the electromagnetically reciprocating apparatus of this kind, operation efficiency becomes maximum when a vibration system having piston assembly 102 and elastic member (coil spring 108) is reciprocated in a resonance state.
More specifically, piston assembly 102 is reciprocated in the resonance state and an amplitude of reciprocating movement thereof is maximum when the following equation (1) is satisfied. That is, maximum operation efficiency of the electromagnetically reciprocating apparatus can be obtained when ##EQU1## where F is the frequency of the commercial electric power source (the number of pulses of DC power source)
M is the mass of piston assembly 102 PA1 Kf is the spring constant of a gas sealed in a sealed space 104a formed in front cylinder 104 partitioned by front piston 104 PA1 Ks is the spring constant of coil spring 108 compressed by rear piston 102c
Then the electromagnetically reciprocating apparatus is used in different areas in which the commercial AC currents have different frequency Fa, Fb (for example, Fa&gt;Fb) the, at first, value of the spring constant (Ks+Kfa) of coil spring 108 and a gas in sealed space 104a, and the mass (M) of piston assembly 102 are set up in order to satisfy the following equation (2) and then make piston assembly 102 reciprocate in maximum amplitude of vibration in the area of frequency Fa: ##EQU2## where: Kfa is the spring constant of a gas in sealed space 104a when the frequency is Fa
Then, if the electromagnetically reciprocating apparatus, in which the various values are set as disclosed above, is used in the area of another frequency Fb, the following equation (3) is introduced: ##EQU3## where: Kfb is the spring constant of a gas in sealed space 104a when the frequency is Fb
From the equation (3), it becomes clear that piston assembly 102 cannot reciprocate in the resonance state because either the spring constant (Ks+Kfb) is too small or the mass (M) of piston assembly 102 is too big.
Therefore, in Japan, for example, which is divided into two areas where the frequency of the commercial electric power sources is 50 Hz and 60 Hz, respectively, in order to make the conventional apparatus obtain the most preferably resonance state in the different frequency areas, the piston weight and the spring constant of coil spring (the elastic member) 108 are changed. This requires manufacturing of various kinds of vibration systems having resonance frequency which are consistent with various kinds of frequency of the commercial electric power sources, as well as independent storage of various kinds of vibration systems.